Hip

Hip Anatomy

The hip joint is the largest weight-bearing joint in the human body. It is also referred to as a ball and socket joint and is surrounded by muscles, ligaments and tendons. The thighbone or femur and the pelvis join to form the hip joint.

Any injury or disease of the hip will adversely affect the joint's range of motion and ability to bear weight.

The hip joint is made up of the following:

Bones and joints

Ligaments of the joint capsule

Muscles and tendons

Nerves and blood vessels that supply the bones and muscles of the hip

Bones and Joints of the Hip

The hip joint is the junction where the hip joins the leg to the trunk of the body. It is comprised of two bones: the thighbone or femur, and the pelvis, which is made up of three bones called ilium, ischium and pubis.

The ball of the hip joint is made by the femoral head while the socket is formed by the acetabulum. The acetabulum is a deep, circular socket formed on the outer edge of the pelvis by the union of three bones: ilium, ischium and pubis. The lower part of the ilium is attached by the pubis while the ischium is considerably behind the pubis. The stability of the hip is provided by the joint capsule or acetabulum and the muscles and ligaments that surround and support the hip joint.

The head of the femur rotates and glides within the acetabulum. A fibro cartilaginous lining called the labrum is attached to the acetabulum and further increases the depth of the socket.

The femur is one of the longest bones in the human body. The upper part of the thighbone consists of the femoral head, femoral neck, and greater and lesser trochanters. The head of the femur joins the pelvis (acetabulum) to form the hip joint. Next to the femoral neck, there are two protrusions known as greater and lesser trochanters which serve as sites of muscle attachment.

Articular cartilage is the thin, tough, flexible and slippery surface lubricated by synovial fluid that covers the weight-bearing bones of the body. It enables smooth movements of the bones and reduces friction.

Ligaments of the Hip Joint

Ligaments are fibrous structures that connect bones to other bones. The hip joint is encircled with ligaments to provide stability to the hip by forming a dense and fibrous structure around the joint capsule. The ligaments adjoining the hip joint include:

Iliofemoral ligament: This is a Y-shaped ligament that connects the pelvis to the femoral head at the front of the joint. It helps in limiting over-extension of the hip.

Pubofemoral ligament: This is a triangular shaped ligament that extends between the upper portion of the pubis and the iliofemoral ligament. It attaches the pubis to the femoral head.

Ischiofemoral ligament: This is a group of strong fibers that arise from the ischium behind the acetabulum and merge with the fibers of the joint capsule.

Ligamentum teres: This is a small ligament that extends from the tip of the femoral head to the acetabulum. Although it has no role in hip movement, it does have a small artery within that supplies blood to a part of the femoral head.

Acetabular labrum: The labrum is a fibrous cartilage ring which lines the acetabular socket. It deepens the cavity increasing the stability and strength of the hip joint.

Muscles and Tendons of the Hip Joint

A long tendon called the iliotibial band runs along the femur from the hip to the knee and serves as an attachment site for several hip muscles including the following:

Gluteals: These are the muscles that form the buttocks. There are three muscles (gluteus minimus, gluteus maximus, and gluteus medius) that attach to the back of the pelvis and insert into the greater trochanter of the femur.

Adductors: These muscles are in the thighs which help in adduction, the action of pulling the leg back towards the midline.

Iliopsoas: This muscle is in front of the hip joint and provides flexion. It is a deep muscle that originates from the lower back and pelvis, and extends up to the inside surface of the upper part of the femur.

Rectus femoris: This is the largest band of muscles located in front of the thigh. They are also called hip flexors.

Hamstring muscles: These begin at the bottom of the pelvis and run down the back of the thigh. Because they cross the back of the hip joint, they help in extension of the hip by pulling it backwards.

Nerves and Arteries of the Hip Joint

Nerves of the hip transfer signals from the brain to the muscles to aid in hip movement. They also carry the sensory signals such as touch, pain, and temperature back to the brain.

The main nerves in the hip region include the femoral nerve in the front of the femur and the sciatic nerve at the back. The hip is also supplied by a smaller nerve known as the obturator nerve.

In addition to these nerves, there are blood vessels that supply blood to the lower limbs. The femoral artery, one of the largest arteries in the body, arises deep in the pelvis and can be felt in front of the upper thigh.

Hip Movements

All the anatomical parts of the hip work together to enable various movements. Hip movements include flexion, extension, abduction, adduction, circumduction, and hip rotation.

Osteoarthritis, also called degenerative joint disease, is the most common form of arthritis. It occurs most often in older people. This disease affects the tissue covering the ends of bones in a joint (cartilage). In a person with osteoarthritis, the cartilage becomes damaged and worn out causing pain, swelling, stiffness and restricted movement in the affected joint. Although osteoarthritis may affect various joints including hips, knees, hands, and spine, hip joint is most commonly affected. Rarely, the disease may affect the shoulders, wrists and feet.

Avascular necrosis, also called osteonecrosis, is a condition in which bone death occurs because of inadequate blood supply to it. Lack of blood flow may occur when there is a fracture in the bone or a joint dislocation that may damage nearby blood vessels. Hip joint is most commonly affected; however, the knee and shoulder may also be involved.

Hip instability can be traumatic or atraumatic. Traumatic instability can be caused by injuries from sports or motor vehicle accidents. These injuries can damage the bony structures, labrum and cartilage of the hip joint and can form loose bodies. It can range from severe dislocation to a simple subluxation (partial displacement) of the hip joint. Atraumatic instability can be caused by overuse or developmental/congenital abnormalities of the hip joint.

Hip fracture is a break that occurs near the hip in the upper part of the femur or thighbone. The thighbone has two bony processes on the upper part - the greater and lesser trochanters. The lesser trochanter projects from the base of the femoral neck on the back of the thighbone. Hip fractures can occur either due to a break in the femoral neck, in the area between the greater and lesser trochanter or below the lesser trochanter.

Inflammation of the joints is referred to as arthritis. The inflammation arises when the smooth covering (cartilage) at the end surfaces of the bones wears away. In some cases, the inflammation is caused when the lining of the joint becomes inflamed as part of an underlying systemic disease. These conditions are referred to as inflammatory arthritis.

Surgical Treatment

Total joint replacement surgery is one of the most advanced successful procedures in patients dealing with severe hip and knee pain. The goal of the surgery is to relieve pain and restore the normal functioning of the joint and help patient resume normal activities.

Traditionally, total hip replacement will be performed through a 10–12-inch-long incision made on the side of the hip. A minimally invasive approach has been developed in recent years where surgery is performed through one or two smaller incisions rather than the single long incision as in the traditional approach. Advantages of the newer approach are lesser muscle dissection, minimal pain, quicker recovery, and faster rehabilitation.

Total hip replacement is a surgical procedure in which the damaged cartilage and bone is removed from the hip joint and replaced with artificial components. The hip joint is one of the body's largest weight-bearing joints, located between the thighbone (femur) and the pelvis (acetabulum). It is a ball and socket joint in which the head of the femur is the ball and the pelvic acetabulum forms the socket. The joint surface is covered by a smooth articular cartilage which acts as a cushion and enables smooth movements of the joint.

Revision hip replacement is a complex surgical procedure in which all or part of a previously implanted hip-joint is replaced with a new artificial hip-joint. Total hip replacement surgery is an option to relieve severe arthritis pain that limits your daily activities. During total hip replacement, the damaged cartilage and bone is removed from the hip joint and replaced with artificial components. At times, hip replacement implants can wear out for various reasons and may need to be replaced with the help of a surgical procedure known as revision hip replacement surgery.

Posterior hip replacement is a minimally invasive hip surgery performed to replace the hip joint. It is also referred to as muscle sparing surgery because no muscles are cut to access the hip joint, enabling a quicker return to normal activity.

Hip replacement surgery is the most common orthopedic surgery performed. It involves the replacement of the damaged hip bone (ball shaped upper end of the femur) with a metal ball attached to a metal stem that is fixed into the femur and attached to the pelvic region. Traditionally, the surgery was performed with a large, open incision and required the patient to stay in the hospital for several days.

Hip implants are artificial devices that form the essential parts of the hip joint during a hip replacement surgery. The hip implants vary by size, shape, and material. Various components of a hip implant may be used for a hip replacement surgery. The components used may depend on the extent of damage to the hip joint, and the preference of the orthopedic surgeon performing the procedure.